Turning the engine in reverse a 1/4" or so won't hurt it. I've never heard that rocking it back and forth can "feel" stretch. That sounds ridiculous to me.

Severe service oil changes are 2500 mile intervals (city driving, winter months). The Castrol 10w-40 and 20w-50 oils aren't rated for diesel service. I wouldn't go more than 3000 miles on those oils. Get Chevron 15w-40 or Mobil 1300S 15w-40 or Shell Rotella 15w-40 (truck diesel oil) next time.

Regards,

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Brian Toscano